Volcanic Vents: Where Lava, Ash and Gas Reach the Surface

A volcanic vent is the place on the Earth's surface where a volcano erupts: lava flows, tephra (ash, lapilli and bombs) and broken rock come out of it, and volcanic gases escape through it. Vents can sit:

• in a summit crater,
• on a volcano's flanks,
• at the base of a cinder cone,
• around the edge of a caldera.

Erupting vents on Mauna Loa in 1984, Hawaiʻi Volcanoes National Park. National Park Service.

Examples in the parks

A summit vent: Redoubt Volcano, Lake Clark National Park and Preserve, Alaska. On 18 December 1989, the vent in Redoubt's summit crater was giving off low-level steam and ash.

Redoubt Volcano’s summit vent, 18 December 1989. U.S. Geological Survey.

A flank vent: the Watchman, Craters of the Moon National Monument and Preserve, Idaho. A vent on the south side of this cinder cone fed lava down a small channel lined with low spatter ramparts.

Ring vents: Mount Mazama, Crater Lake National Park, Oregon. The climactic eruption that formed the Crater Lake caldera came from ring vents along the fractures where the summit collapsed, sending pyroclastic flows outward. They now lie beneath the lake, because landslides soon after the eruption widened the caldera beyond them.

Ring vents of Mount Mazama’s caldera eruption; arrows show the pyroclastic flows. Adapted from Bacon and Wright, 2017, U.S. Geological Survey.

Linear vents

Many vents are roughly round, but some are long and narrow. During the May 2018 eruption of Kīlauea, a long fissure vent opened on the lower East Rift Zone, outside the boundary of Hawaiʻi Volcanoes National Park.

A linear fissure vent during Kīlauea’s 2018 eruption. U.S. Geological Survey Hawaiian Volcano Observatory.

Vent plugs

At the end of an eruption, a vent is usually sealed by a plug of solidified magma. The Novarupta dome did this at the close of the 1912 eruption in what is now Katmai National Park, the eruption that created the Valley of Ten Thousand Smokes.

The Novarupta dome in June 2006. U.S. Geological Survey.

Sources

• National Park Service, "Volcanic Vents"; rewritten in hubnx's own words. Photographs and diagram: National Park Service and U.S. Geological Survey.